I’ve been looking for an answer to the same question, and it doesn’t seem like there’s a good way to do it inside of wordpress.
Here’s one way that seems to work, if you have access to your database (although it’s not a proper solution, IMHO):
Using something like phpMyAdmin to access your database, you can go into the “options” table and change the value of “admin_email” to contain both addresses, separated by a comma. Like “[email protected],[email protected]”.
There’s got to be better way than that, though…